My experience is pretty much like Lisa's here in the NW burbs of Boston. Most drivers are OK, as there are so many cyclists around, they are used to us. However, you don't need to go too far to the east to find more aggressive or clueless drivers. Also, the beach areas are pretty bad for cyclists.
There have been some issues with cyclists in Carlisle (the town next to me), but I would say it is the police who are being aggressive. I know someone who got a $50.00 ticket, but he was riding like jerk.
Then there was the guy who told my husband to "Get a car," when he was riding home from work last week. He was taking the lane, on a very pot holed winding main road (Rt. 126 in Lincoln), going about 24 mph, which is not much slower than cars go.